Question

Your cousin just started a part-time job at a blood bank. he tells you that a surprisingly large number of native americans come in to donate blood. you explain to him that, based on what you learned in physical anthropology class, this is not all that surprising because

Answer 1

I believe the answer is: owing to a founder effect, many Native American populations have high frequencies of the O blood type.

While any other blood type can only donated to others with similar blood type (blood type A could only be donated to blood type A, blood type B could only be donated to blood type B, etc), that is not the case with blood type O.

The O blood type is what people referred to as a universal donor, which mean it can be donated to any other blood types, which make them perfect for blood banks.